Conventional fluid pressure regulators are generally of the type which utilizes a cone or ball type valve member seating into an orifice with just enough tapered seat width to prevent wear. The shiftable valve member is biased with a coil spring and the pressure seal is usually a formed cup, an O-ring, a diaphragm or bellows.
The construction of the shiftable valve member is such that it tends to bend or drag because of high internal friction and to shift laterally in relation to the seat due to a degenerative turbulence effect, thereby causing improper mating and friction between the valve members. For the above reasons and others to be mentioned later, the outlet pressure of a fluid pump cannot be reliably maintained within a desired range of values for variations in volume rates of fluid flow therethrough. Generally, the best regulation is 10 to 20 percent. This means that the pressure at the outlet of the fluid pump varies by this amount with changes in the output load requirement of the pump.
When conventional regulators under fixed loads and volume rates are cycled on and off, the pressure at the output of the pump will tend to vary at random from zero to 20 percent from the desired set point. Also, the pressure set point may change hours or days after the pressure has been set.
Moreover, popular seal cup type regulators respond very slowly due to internal friction so that pumps using conventional regulators need air accumulators to reduce high peak pressures in the output flow of the pump. Such accumulators add to the overall cost of the system. Conventional seal cup designs are limited to approximately 160.degree.F. because of the materials and general shape forming the same. Metallic diaphragm seals will stand high temperature, but are not suited for piston pumps at high pressure due to structural fatigue of the diaphragms. Coil springs are subject to breakage and tend to side load the shiftable member causing serious misalignments.